It is generally known that, in hot strip rolling, after it runs out of the last stand of the finishing train, the finish-rolled hot strip is transported from the delivery table through a cooling line, preferably a system of spray-water nozzles, to a coiling device. The hot strip is wound up by the coiling device into coils. In the region upstream of the coiling device, the hot strip may be guided on the delivery table by side guide shoes, which can be hydraulically adjusted laterally onto the strip edges, in order to align the rolled hot strip for running into the coiling device. In a corresponding way, the side guide shoes are in contact with the strip edges of the hot strip during the coiling operation.
Arranged at the end of the delivery table is a driving device, which substantially comprises a lower driving roller, which is mounted in the frame of the coiling device, and an upper driving roller, which is mounted in a driver rocking arm. The upper driving roller can be pivoted by means of hydraulic cylinders for setting and adjusting the gap between the driving rollers. With the aim of stabilizing the running of the strip, convex lower driving rollers or else driving rollers with a cylindrical central part and respectively conical roller ends are primarily used. The main functions of the driving device, including its drives, are to tension the beginning of the rolled strip coming from the finishing train, direct the incoming tip of the strip in the direction of the coiling device and ensure the draw-back counter to the coiling device during the coiling operation.
The main components of the coiling device are an expanding mandrel for winding up the rolled strip, back-up rollers and guide trays for guiding the rolled strip during the winding operation and also a mandrel drive. The free mandrel end (coil drawing-off side) is generally supported during coiling by a mandrel bearing which can be swung in.
To initiate the winding operation, the tip of the hot strip coming from the finishing stand is deflected by the pair of driving rollers from the plane of the delivery table downward toward the winding mandrel. Then, the back-up rollers and the guide trays of the coiling device pass the beginning of the strip several times around the rotating mandrel. The mandrel comprises a number of segments, which are continuously expanded shortly after the tip of the strip arrives, until the strip is wound into lays of coil lying firmly one on top of the other with frictional engagement. The main functions of the coiling device are to ensure the frictional connection of the beginning of the strip and the mandrel, to carry the coil produced during winding and to apply defined strip tension to the strip during the winding.
Furthermore, German Offenlegungsschrift DE 38 28 356 A1 already discloses a method for influencing the position of the hot strip which is fed to a coiling device by a pair of driving rollers, and a driving device for carrying out this method. In the case of this method of controlling the strip position, the strip guidance for the coiling device takes place exclusively by an asymmetric adjustment of the gap between the driving rollers by means of a pivotable upper driving roller. For this purpose, the upper driving roller is mounted in a driver rocking arm, which has hydraulic adjustment and balancing. This also has the result that the side guide shoes are opened during the coiling operation.
The adjusting effect of this driving device with respect to the hot strip is based on a shift in the location of the point of action of the strip tensioning force and the resultant uneven elastic strip lengthening (bending) caused by pivoting of the upper driving roller. Pivoting of the upper roller leads to opening of the driver gap on one side and consequently a shift in the point of action of the pressing force which the driving rollers exert on the strip. The point of action of the force, which in the case of a symmetrical driver gap lies in the center of the installation, is now shifted by a distance from the center of the installation in the direction of the unopened side of the driver gap. As a consequence of this, the strip draw-back force resulting from the braking moment of the driving device likewise acts at a distance from the center of the installation on the strip which until then is still running centrally. This force-introducing situation brought about by the pivoting/tilting of the upper driving roller results in a moment exerted on the still centrally running strip that causes elastic transverse bending of the strip. As a consequence of this deforming of the strip, the longitudinal fibers of the strip in the region of the driving device are oriented at an angle in relation to the center axis of the installation or at an angle in relation to the axes of the driving rollers. Consequently, a strip led in frictional engagement over a driving roller tends to follow the curves of the path of the points of the roller shell in the contact region. This means in the present case that the strip does not for instance run through the driving device in a path following the longitudinal direction of the strip fibers, but instead the point of the strip located at the given instant in the contact region is transported in the direction of the circumferential speed vector of the roller at the contact point, that is in the direction of the longitudinal axis of the installation. This results in a transverse shift of the strip in the driving device. This shift of the strip also causes a gradual increase in the distance between the point of action of the driver draw-back force and the center point of the tension on the coil at the strip run-on point. However, with great tilting of the upper driving roller, the distance from the center of the installation becomes considerably greater than the transverse shifts of the strip occurring, so that the influence of the resultant change in the distance from the center of the installation can be ignored.
The strip position control system disclosed by the aforementioned German Offenlegungsschrift DE 38 28 356 A1 substantially comprises a strip edge detection system, a strip position controller and a hydraulic adjustment of the upper driving roller with force and tilt control. The influencing of the strip position takes place by the pivoting/tilting of the upper driving roller in a way corresponding to the mechanical principles described above. The system deviation for the strip position controller is formed from the position of the strip edge at the given instant, which is detected by means of strip edge scanning, and the setpoint position value, which is determined from the strip width and the dimensions of the installation. The output variable of the strip position controller is the setpoint value of the driving roller tilt, which is prescribed for the driving roller adjustment. Since no contact occurs between the shoes and the strip when the side guide shoes are open, both the customary wearing of the shoes and damage to the edges of the strip caused by the side guide shoes are avoided.
Operational tests have shown that strip guidance by the driving device with the side guide shoes open is possible in principle for hot rolled strips up to a thickness of approximately 5 mm. However, the quality requirements for the wound state are not completely satisfied with this method. The contour of the coil end face showed limited but inadmissible residual undulations (range of variation around ±10 mm). During unthreading from the finishing stand, winding offsets occur. The following causes are decisive for these defects, i.e. for the lateral shearing out of lays of coil:
Essential for the function of the driving device as an actuator for the strip position controller is the influencing of the delivery angle of the strip (angle between strip center line and driving roller axis). In the case of curved strips (“sabre form”), the angle caused by the curvature has the effect of a disturbance, i.e. the angle from the strip curvature is not taken into account when generating the manipulated variable and falsifies the latter in an initially undetected magnitude.
Since the armature current of the driving roller drives is controlled by the higher-level drive control, and can consequently also be limited, if a current limit that is too low is prescribed, the resultant tension in the strip between the mandrel and the driving device is too low, so that the aimed-for actuating effect cannot be achieved by pivoting the upper driving roller in order to drive the strip into the setpoint position.
An abrupt relaxation of the tension of the strip also takes place when the strip is unthreaded from the finishing stand, which can cause instances of slippage in the driver gap and consequently cause a winding offset in the coil.
Furthermore, a method for measuring the surface geometry of hot strip by generating lines on the strip surface by means of a light source is described in German Patent DE 197 09 992 C1. This method is intended to make simple and effective detection of the flatness of the strip possible, in order to use this for a more sensitive control of rolling and coiling parameters. A pattern of lines is projected by means of a slide projector on the measuring surface, the hot strip or the end face of a coil in the process of being produced, and is detected by means of a CCD camera (charge coupled device). The projector is in this case arranged above the hot strip and projects the pattern of lines at an angle to the vertical onto the surface of the hot strip, so that the lines preferably extend transversely in relation to the surface of the strip and consequently cover the entire width of the strip.
The CCD camera detects the lines running transversely over the surface of the strip. If the strip is absolutely flat, a uniform pattern of straight lines with unchanged line spacing is produced. Deviations of the surface of the strip from the ideal plane cause a change in the line spacing in the region of the unevenness. This change is detected by the camera and can be computationally converted in a simple way into differences in height by a comparison with a reference pattern. In a way similar to measuring flatness on the running strip, the measuring system can be used to monitor the flatness of the end faces during coiling. The end face of the coil building up in the coiler in this case corresponds to the surface of the strip. This measuring method makes possible a rapid online determination of the actual differences in height of the surface of the strip and consequently allows real-time detection and control of continuous portions of strip. This has the advantage that the measurement results allow the rolling and/or coiling parameters to be adapted immediately after an unevenness occurs. Even a transverse convexity of the strip can be determined in this way. Conventional measuring systems detect only the fiber length of the strip. What is more, the measuring lines can be adapted with respect to their intensity and line thickness to different conditions.
To sum up, it is consequently found that there continue to be occurrences of lateral shearing out of lays of coil during the coiling up of rolled strip, which are caused by transverse movements of the rolled strip to be coiled up and lead to uneven end faces of the coil. In the course of the further processing and transporting of such coils, the protruding strip edges are susceptible to damage. Owing to these instances of damage, additional costs may arise in further processing or losses in revenue may occur. In addition, the conventional way, described at the beginning, of guiding the rolled strip during coiling by means of side guide shoes entails relatively high expenditure on maintenance, since the side guide shoes are subject to increased abrasive wear by the strip edges of the rolled strip to be guided.